Research And Implement Of Audio Communication Sub-System Of Multi-Media Communication Based On DM642

With the development of network communications and multimedia technologies, the application of delivering audio and video over Internet is getting more and more popular, and today come forth various audio and video systems. Moreover, with the rapid improvement of DSPs processing ability, audio and video processing platform quickly trends to miniaturization. The research on audio and video real-time communications based on embedded DSPs system becomes a hotspot.This paper mainly research on audio communication system which is part of multimedia communication. Firstly,To master the status in quo about audio communication technologies through consult information, study and analysis existented problem at present about the audio communication technologies and related solutions. Secondly, build the audio communication system based on the DM642 platform, the keystone and difficulty including these aspects below, building of the system based on the hardware platform, replant and optimize of the G.729A coder and decoder algorithm, the design and realization of audio communication control signaling based on SIP stack, the transport technologies on the Internet of the speech signal, the design of multi-tasks and task synchronize mechanism and so on. Try to master the core technology of audio communication via achieve the system, and to get ready for explore audio and video systems in the future.This system is built on TI DM642EVM platform. TI DM642 is a kind of DSP chip designed for multimedia applications. Its core clock is up to 600MHz, and it has 8 parallel operation units, its processing ability is up to 4800MIPS. For multimedia applications, DM642EVM integrates 3 configurable video ports, McASP for audio applications, 10/100Mb/s Ethernet MAC and so on.On the realization of the system, this system use CCS, adopt DSP/BIOS real-time OS, BSL (Board supported library), DDK (Driver develop kit), RF5 (Reference framework 5), CSL (Chip supported library) and other supported module to develop the software. Using of these module improving the programme efficiency, shorten the system implement period. And the system using C language to design and realize the audio communication system.This system realized the point to point and point to multi-point audio communication system, each endpoint of the system is based on the DM642 platform. Each endpoint is consisted of two parts, signaling module and media module. Signaling module includes three tasks, signaling send and receives task and uart task. Media module including six tasks, audio capture task, audio coder and decoder task, audio send and receive task, and audio player task. Tasks of signaling module are synchronized by extern variable; Tasks of media module are synchronized using SCOM mechanism.SCOM mechanism is a kind of synchonize mechanism which is offered by RF5. It build absolute message unilateralism channel for every task which need to synchronize with other tasks to realize the synchronize control, and use the message structure to realize the share and mutex of the resource. The disposal of the audio data between tasks in this system uses SCOM to realize synchronization. This system is to develop the software on the hardware platform, to accomplish the design and realization of nine modules talked above. The system is devided into two parts, signaling module and media module.The signaling module is consisting of keyboard and UART. In this system, using the keyboard to simulate dial to trigger signaling, to achieve call setup, media negotiation and call realease and so on.The media module is consisting of audio codec, DM642 and ethernet chips. After the setup of the signaling, the media modules achieve audio capture, process, and transport and so on. The principle of the system is this, firstly,control the AIC23 audio coder and decoder chip and audio port to realize the audio capture, keep the audio data captured in the capture buffer and compress the captured audio data using G.729A algorithm. Secondly, use the SCOM to transport audio data between tasks and use ethernet to complete the audio communication between DM642 and PC or DM642 and DM642. Finally, the receive endpoint play the audio after a series of reverse operation to realize the IP phone system based on the embed system.At last, this pater tests the performance of the system and proposes related methods to improve the Qos performance of the system. First, the buffer mechanism of send and receive tasks, Second, audio coder and decoder algorithm. Then study these two methods separately and give the test result. This system adopts G.729A audio coder and decoder algorithm which is popular today. The algorithm can accomplish the speech compression in very low bit rate, suit for the demand of the IP phone today. In this system we wrapper the algorithm in a CELL according to the RF5 and optimize it according to the characters of the hardware platform. This paper also compare the former and after performance and prove that the performance after optimize is better than before.According to what we have talked above, we can concluded that this article researches some key technologies about the audio communication based on embed system, designs and achieves a audio communication system and point to point and point to multi-point control signaling based on DM642 hardware platform.However realized the improvement on the problems exist in the system and proved that the effect is very well. For the sake of the time, this system is not perfect, and the author will improve it during afterward works.